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is drifted by humid wind and collects at a point where the wind velocity is reduced, but is not calm. In traveling over the crest of a ridge, drifting snow frequently forms cornices (see fig. 8). These occur in the calm triangular region between the air current flowing over the top of a ridge and the eddy current drawn up the lee side of the ridge by the main current of air. Drifting snow carried by the main current settles, in part, into this comparatively calm region, and builds out the cornice, either by the interlocking of the crystal branches, or by formation of a wind slab. Snow carried past this calm region before dropping out of the main air current falls below the cornice and forms a drift, generally known as a snow cushion. |
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